1. Field of the Invention
The present invention generally relates to an image processing system in which two or more image forming apparatuses such as digital copiers, scanners, printers and facsimile machines are connected to each other and, more particularly, to a two-way image processing system including such apparatuses.
2. Discussion of the Background
Recently, with the introduction of the digital technology in copiers, processing or editing of image data using an image memory has become available. For example, rotation of an image or repeating of an image is possible by controlling read addresses of the image. Images from a plurality of original documents may be copied to one sheet of transfer paper by controlling write addresses of the images. In order to implement such facilities, a copier should generally be provided with an image memory for at least a page of an original document.
Another aspect of note in the digital copiers produced recently is that the facilities provided by a plurality of copiers are integrated. For example, Japanese Laid-Open Patent Application No. 321976 discloses a method whereby a plurality of digital copiers are connected by a cable so that, when a first copier is in use outputting a copy and a second copier is not used, image data is transferred to the second copier so that the second copier can also output a copy.
Various methods for transferring image data are known. For example, in asynchronous transfer of the SCSI system, handshake between devices involved in the transfer is performed for each transferred data unit. Data is transferred by exchanging a data request signal and a data acknowledgement signal. However, such a method of transfer, when performed between two digital copiers, causes a slow response especially when the cable is long, causing the transfer time to be significantly extended.
According to a conceivable method of transfer, a transmitting copier may scan an original document at a regular speed so that image data is output in synchronization with a clock using a raster system. The transfer time in this case would be significantly reduced as compared to the transfer time in the SCSI system. However, the latter method has a disadvantage in that received data may not be properly processed when a transmitting copier and a receiving copier are of different types or when the performance of the copiers are not suitable.